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Challenge: An operator in the Gulf of Mexico drilled a 10,270 ft (3,131 m) hole in 1000 ft (305 m) of water to TD. They set 7 in. casing from 9,369 ft (2,856 m) MD to surface and ran 5 in. liner for production. While running the liner, it got stuck at 9,971 ft (3,040 m), about 300 ft (91 m) off bottom and within 10 ft (3 m) of the top of the 174 ft (53 m) thick pay interval. The rig experienced frequent severe barite sag while drilling the 6 ⅛ in. hole below the 7 in. casing. This is believed to have contributed to sticking the 5 in. liner. When it was determined that the liner couldn’t be pulled free, it was cemented in place. Subsequent discussion focused on two possibilities: a second side-track or an open hole completion with the liner at current depth. The decision hinged in part on the availability of a reservoir drill-in fluid for the application. The operator asked M-I SWACO to propose a water-based Reservoir Drill-In Fluid (RDF), in the 13.1 to 13.5 lb/gal (1.57-1.62 s.g.) density range.

Solution: M-I SWACO was able to offer DIPRO and DIPRO SF systems for this project. DIPRO RDF is unique among water-base reservoir drill-in systems. DIPRO RDF is unique among water-base reservoir drill-in systems because it relies upon only derivatized starch for viscosity. It yields fully in high-salinity chloride brine and provides the functionality required of a water-base drill-in fluid at higher density. Among the major benefits of DIPRO RDF are very high low-shear rate viscosity (LSRV) and ease of maintenance in the field.

Result: Following an initial meeting with operator engineers and managers, M-I SWACO went to work in the Houston Technical Services laboratory to prove the fluid. In less than 48 hours, the laboratory was able to provide rheology data on the 13.2 lb/gal (1.58 s.g.) DIPRO fluid, an API filtration test result, a successful production screen test (PST) result, as well as, results of compatibility testing between the drilling mud and RDF; between the RDF and the visco-elastic surfactant (VES) gravel pack carrier fluid; and between the VES with the RDF breaker fluid, BREAKDOWN HD. The Tech Services lab also provided successful breaker test results and a cleaning test result which proved that the severe emulsion formed by a 50:50 blend of the drilling mud and DIPRO RDF could be easily broken and removed. Within 72 hours of the planning meeting at the operator’s office, 1000 bbl of 13.2 lb/gal (1.58 s.g.) DIPRO RDF was blended for load-out to location.

After cleaning out the open hole with DIPRO RDF, solid-free DIPRO (DIPRO SF) displaced the open hole. A viscous weighted spacer and a cleaning solution of DIPRO in completion brine preceded the DIPRO SF into the open hole. 13.1 lb/gal (1.57 s.g.) CaCl2/CaBr2 completion fluid displaced out the remaining DIPRO RDF from the cased hole. The gravel pack was performed without incident, using BREAKDOWN HD in the carrier fluid. Two weeks after the gravel pack, the well produced at twice the expected production rate, with anticipated production ramp-ups scheduled.

Operations from drilling out the liner shoe through completion of the open hole gravel pack took 3 ½ weeks. DIPRO and BREAKDOWN HD allowed the operator to complete their original reservoir target and avoid the expense of sidetracking the interval.

The operator drilled out the liner shoe into the top of the sand with SBM, then picked up just above the shoe and displaced the well to DIPRO RDF. During the pre-job testing phase M-I SWACO informed the operator that the invert emulsion drilling mud and DIPRO RDF were not compatible fluids. The recommendation was to enter the open hole with DIPRO RDF and slowly displace out the drilling mud. The operator entered the open hole section with a bit and motor and MWD and washed and reamed from the shoe to TD with pump rates between 2 and 3.5 bbl/min while rotating pipe at 25 rpm for 36 hours. The wellbore contained one severe dogleg between about 3,550 – 4,825 ft (1,082 – 1,471 m) MD / 3,525 – 4,475 ft (1,075 – 1,364 m) TVD; then held a 74º angle relative to vertical for ~ 4,400 ft (1,341 m) MD / ~ 1,100 ft (335 m) TVD.

Two objectives were served by lowering into the open hole slowly with the bit: one, the operator’s concern that the BHA not create an accidental sidetrack, but stay within the existing borehole; and two, that hole cleanout operations minimize the amount of invert emulsion drilling mud assumed into the DIPRO RDF, especially in the open hole section. In the process, the bit followed the original hole path. Returns were consistently loaded with cement, shale, barite and formation sand, but DIPRO RDF properties maintained at competent levels throughout. The DIPRO RDF maintained its rheological properties with infrequent additions of DIBALANCE and DITROL despite the constant flow of contaminants.

Field engineers kept LSRV and YP at relatively low levels during the hole cleanout phase due the potential for increasing viscosity when SBM was taken into the DIPRO RDF system. LSRV was maintained near 22,000 and YP near 15 throughout by adding DIBALANCE and DITROL when required. Density was maintained by the addition of calcium chloride flake.

The gravel pack consisted of a low-rate procedure pumping through the screen, sanding out from the screen outward. BREAKDOWN HD, a calcium tolerant chelant breaker was added to the brine gravel pack carrier fluid at 15% v/v during the operation. It was allowed to soak while the upper completion equipment was installed in the well. Production commenced without any problems.